drm/amd: Drop error message about failing to load DMUB firmware

The error path for DMUB firmware loading is unnecessarily noisy.
When a firmware is missing 3 errors show up:
```
amdgpu 0000:07:00.0: Direct firmware load for amdgpu/green_sardine_dmcub.bin failed with error -2
[drm:dm_early_init [amdgpu]] *ERROR* DMUB firmware loading failed: -19
[drm:amdgpu_device_init [amdgpu]] *ERROR* early_init of IP block <dm> failed -19
```

The error code for the device init is bubbled up already, remove the
second one.
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

@@ -4754,8 +4754,6 @@ static int dm_init_microcode(struct amdgpu_device *adev)
 		return 0;
 	}
 	r = amdgpu_ucode_request(adev, &adev->dm.dmub_fw, fw_name_dmub);
-	if (r)
-		DRM_ERROR("DMUB firmware loading failed: %d\n", r);
 	return r;
 }